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41 votes
3 cookies and 5 brownies cost $19; 2 cookies and 10 brownies cost $26. How much do 13 cookies and 6 brownies cost?

User Ramaraj T
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1 Answer

27 votes
27 votes

ANSWER

$51

Step-by-step explanation

Let the cost of one cookie be c.

Let the cost of one brownie be b.

3 cookies and 5 brownies cost $19. This means that:

3 * c + 5 * b = 19

3c + 5b = 19 ___(1)

2 cookies and 10 brownies cost $26. This means that

2 * c + 10 * b = 26

2c + 10b = 26 ____(2)

We have two simultaneous equations:

3c + 5b = 19 ___(1)

2c + 10b = 26 ____(2)

From (2):

2c = 26 - 10b

Divide through by 2:

c = 13 - 5b

Put this in (1):

3(13 - 5b) + 5b = 19

=> 39 - 15b + 5b = 19

Collect like terms:

-15b + 5b = 19 - 39

-10b = -20

Divide through by -10:

b = -20 / -10

b = $2

Remember that:

c = 13 - 5b

=> c = 13 - 5(2)

c = 13 - 10

c = $3

Therefore, one cookie costs $3 and one brownie costs $2.

Therefore, the cost of 13 cookies and 6 brownies is:

13 * 3 + 6 * 2

=> 39 + 12

=> $51

13 cookies and 6 brownies cost $51

User Hasseg
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